Fiber optic cables and assemblies should preserve optical performance when deployed in the intended environment while also satisfying any other requirements for the environment. Indoor cables for riser and/or plenum spaces, for example, may require certain flame-retardant ratings as well as mechanical requirements. Mechanical characteristics such as crush performance, permissible bend radii, and temperature performance in part determine how installation and use of the cable in the installation space affect optical performance of the cable.
Certain conventional indoor riser applications use a fiber optic cable disposed within a metallic interlocking armor layer. “BX armor” or “Type AC” cables utilize such armors. BX armor is wound spirally about the fiber optic cable so that the edges of the adjacent wraps of armor mechanically interlock to form an armor layer. Interlocking armors are robust but expensive to install. In particular, the metallic armor must be grounded in order to meet electrical safety standards. FIG. 1 shows several prior art examples of interlocking armored cables 10 having a metallic (typically aluminum) armor layer 12. The metallic armor layer 12 must be grounded, for example, in order to comply with the National Electrical Code (NFPA 120) safety standard. Additionally, the metallic armor 12 can be plastically deformed (i.e., permanently deformed) under crush loads, which can pinch the cable and cause permanently elevated levels of optical attenuation that remain after the crush load is released.
Manufacturers have attempted to design dielectric armor cables to overcome the drawbacks of conventional metallic armor constructions. U.S. Pat. No. 7,064,276 discloses a dielectric armor cable having two synthetic resin layers where the hard resin layer has a continuous spiral groove cut completely through the hard resin layer along the length of the armor. The hard adjoining edge portions of the spiral groove abut to inhibit bending below a certain radius. However, one skilled in the art would recognize this design does not provide the craft with all of the desired features. Moreover, it can be difficult for the craft to recognize the cable of the '276 patent as an armored cable layered because it has a smooth outer surface, whereas conventional metal armored cables as depicted by FIG. 1 are easily identified by the craft.